1. Field of the Invention
The present invention relates to an ejector cycle system with a high-pressure side refrigerant pressure equal to or higher than the critical pressure of refrigerant. The ejector cycle system has an ejector in which high-pressure side refrigerant is decompressed and expanded so that gas refrigerant evaporated in an evaporator is sucked therein, and a refrigerant pressure sucked into a compressor is increased by converting an expansion energy to a pressure energy.
2. Description of Related Art
In recent years, instead of flon refrigerant, the other refrigerant is used in a vapor compression refrigerant cycle. For example, U.S. Pat. No. 5,245,836 describes a vapor compression refrigerant cycle using carbon dioxide. However, in this case, because it is necessary to increase high-pressure side refrigerant pressure to be equal to or higher than the critical pressure, a necessary power for operating a compressor becomes larger, and coefficient of performance of the refrigerant cycle is decreased.
In view of the foregoing problems, it is an object of the present invention to provide an ejector cycle system with a high-pressure side refrigerant pressure equal to or higher than a critical pressure, which improves coefficient of performance (COP) of a refrigerant cycle.
According to the present invention, an ejector cycle system includes a compressor for sucking and compressing refrigerant, a radiator for cooling refrigerant discharged from the compressor, an evaporator in which refrigerant is evaporated by absorbing heat, an ejector which decompresses and expands refrigerant from the radiator to suck gas refrigerant evaporated in the evaporator and converts an expansion energy to a pressure energy to increase a refrigerant pressure to be sucked into the compressor, and a gas-liquid separator for storing refrigerant and for separating refrigerant into gas refrigerant and liquid refrigerant. In the refrigerant cycle system, a refrigerant pressure before being decompressed in the ejector is equal to or higher than the critical pressure of refrigerant. When refrigerant is used in a super-critical area (trans-critical area), a ratio of a specific enthalpy difference to a pressure change (xcex94P) becomes larger, and a pressure difference during the decompression and expansion becomes larger, as compared with a case using flon as refrigerant. Thus, in the present invention, the expansion energy is sufficiently recovered during the decompression. Further, in the ejector, the pressure of refrigerant discharged from the ejector is increased from a middle pressure higher than a pressure within the evaporator to a pressure lower than the critical pressure. Therefore, consumption power of the compressor can be reduced. In the super-critical area of refrigerant, because a density of gas refrigerant is approximately equal to that of liquid refrigerant, refrigerant decompressed and expanded in the ejector has approximately equal speed in both gas refrigerant and liquid refrigerant. For example, when carbon dioxide is used as refrigerant, an ejector efficiency is increased approximately twice, as compared with a case where flon is used as refrigerant. As a result, in the ejector cycle of the present invention, because the refrigerant pressure before being decompressed in the ejector is equal to or higher than the critical pressure of refrigerant, the coefficient of performance of the ejector cycle system can be improved.
Preferably, the gas-liquid separator is disposed so that gas refrigerant in the gas-liquid separator is supplied toward a suction side of the compressor and liquid refrigerant in the gas-liquid separator is supplied to the evaporator, and the ejector cycle system further includes a heating unit which heats refrigerant sucked into the compressor. Therefore, temperature of refrigerant sucked into the compressor can be increased, the refrigerant temperature discharged from the compressor is also increased, and the radiator capacity and the efficiency of the ejector cycle system can be improved.
Preferably, an ejector efficiency control unit is provided to control a converting efficiency of the energy in the ejector. Further, flow amount adjusting means for adjusting a flow amount of refrigerant flowing into the ejector is provided. Thus, the ejector cycle system operates while the ejector efficiency is improved.
Further, a control valve is disposed in a refrigerant passage of the ejector cycle system so that refrigerant pressure before being decompressed in the ejector is equal to or higher the critical pressure of refrigerant. Therefore, the ejector cycle system operates while the ejector efficiency is improved. preferably, the control valve and the ejector are integrated. Therefore, the structure of the ejector cycle system can be made simple. More preferably, the ejector includes a nozzle in which a pressure energy of high-pressure refrigerant flowing from the radiator is converted to a speed energy so that refrigerant is decompressed and expanded, and a pressure increasing portion in which the speed energy is converted to the pressure energy so that the pressure of refrigerant is increased while refrigerant discharged from the nozzle and refrigerant sucked from the evaporator are mixed. The control valve can be integrated with the nozzle of the ejector.
Preferably, the gas-liquid separator has a tank portion in which refrigerant is stored while gas refrigerant and liquid refrigerant are separated from each other, and a part of the ejector is integrated with the tank portion. For example, the ejector is disposed so that refrigerant flows within the ejector from a lower side upwardly, and the ejector is integrated with the tank portion so that an outlet of the ejector is positioned upper than a liquid surface of refrigerant within the tank portion. In this case, a collision wall to which refrigerant flowing from the outlet of the ejector collides can be provided. Alternatively, the ejector is integrated with the tank portion so that the outlet of the ejector is positioned upper than the liquid surface of refrigerant within the tank portion, and refrigerant discharged from the outlet of the ejector collides with an inner wall surface of the tank portion.